1. Field of the Invention
The present invention relates to non-linear optics and more specifically to electro-optical modulators for highest frequencies.
2. Description of the Related Art
An electro-optical light-modulator for the modulation of the 0.633 .mu.m-radiation of a He-Ne-laser with the 311-.mu.m-radiation (964 GHz) of a HCN-laser in a LiNbO.sub.3 -crystal is known from a publication of I. P. Kaminow, et al., Applied Physics Letters, 16, No. 11, June 1, 1970, pages 416-418. The crystal has the form of a thin platelet with parallel main surfaces. The modulating 311-.mu.m-radiation falls through a lens perpendicular to the main surfaces through the crystal platelet, while the 0.633 .mu.m-"carrier"-radiation enters into a narrow side of the crystal platelet at such an angle to the main surfaces that it is totally reflected once at each of the two main surfaces. The modulating radiation and the modulated radiation proceed through the crystal at such an angle with respect to each other that a phase-matching is achieved: i.e., the optical wave-front of the wave to be modulated "sees" a constant modulation-field-amplitude in the ideal case. If the amplitude of the modulation field produced in the crystal by the modulating radiation (upon which the local index of refraction of the crystal depends) would oscillate during the traversal through the crystal of the optical wavefront of the wave to be modulated, then this would lead to an undesirable obliteration of the retarding or accelerating contribution, respectively, of the modulation field.